"We have joined together in an unprecedented team of atmospheric physicists, solarterrestrial
physicists and particle physicists, to offer CERN the opportunity to make
a major contribution to environmental science. Clouds are the engines of the weather,
yet they are only sketchily understood at the microphysical level. Now satellite observations
give empirical evidence for an astonishing link between high-energy physics and
meteorology, namely that cosmic rays from the Galaxy may influence cloud formation and
behaviour.
If this link between cosmic rays and clouds is real, it provides a major mechanism for
climate change. Duringthe 20th Century the cosmic rays reachingthe Earth diminished
by about 15% as a result of increasingvig our in the solar wind, which scatters the cosmic
rays. The inferred reduction in cloud cover could have warmed the Earth by a large
fraction of the amount currently estimated to be due to man-made carbon dioxide. In
that case, the effect of carbon dioxide may have been overestimated. If, on the other hand,
the link to cosmic rays proves to be illusory, present diplomatic efforts to curb emissions
of carbon dioxide will be more strongly supported scientifically. Settling the issue, one
way or the other, is therefore an urgent task.
To find out whether cosmic rays can affect cloud formation, and if so how, we propose
to simulate the cosmic rays with a beam of charged particles from CERN’s Proton
Synchrotron, in the CLOUD experiment. The beam will pass through a cloud chamber
where the atmosphere is to be represented realistically by moist air charged with condensation
nuclei and trace condensable vapours, and chilled by expansion. We shall be able
to compare processes when the beam is present and when it is not.
Our team brings to the planning of the CLOUD experiment a thorough knowledge of
atmospheric and cloud science, derived from field and laboratory experiments, airborne
data-gathering, satellite observations, and microphysical theories. We also possess considerable
experience with cloud chambers and their optical readout, and with the mass
spectrometers and aerosol particle detectors required for chemical and physical analyses
of aerosols and ions. The design of the cloud chamber draws on CERN’s own experience,
notably with the BigEurop ean Bubble Chamber.
Space research has shown how ”bigscience” can make spectacular contributions to
knowledge of the environment by bringing together experts from different disciplines. As
an analogous multidisciplinary team for particle physics, we do not claim total originality.
More than 100 years ago C.T.R. Wilson invented the cloud chamber to investigate weather
phenomena. It evolved into a prime instrument for particle physics. Now the wheel of
history turns and we go back to Wilson’s concept to investigate the possibility that the
Earth’s atmosphere acts like one bigcloud chamber that echoes the whims of the Sun."